With wide application of micro-electrical equipment, especially the mobile communication equipment, charging device for battery becomes the necessity of the mobile equipment. A high-frequency circuit is usually used to design and build a charger for conveniently carrying and the self-adaptation the AC100V˜240V mains voltage, therefore the safety performance of the charger appears particularly important. A current-limiting resistor against over-current and over-temperature is the key component for the safety of the high-frequency circuit. The present invention provides to meet the demand of safety requirements, further achieving reliability and quick response.
Although the wirewound resistor also has an over-current fuse function, the resistor wire is applied with a high melting point alloy and the alloy wire of the wirewound resistor will melt to realize fuse function only if subjected to a current which is over 20 times of the rated current. However, in actual application, when the load is abnormal, the current of the wirewound resistor is often unable to reach the current level which the wirewound resistor material can melt, therefore cause the fuse function of the wirewound resistor can't be realized, while the temperature of the wirewound resistor reaches 300˜500° C.
This is a serious problem and dangerous condition for the charger. Under these conditions, people use an external contact type thermal fuse connected in series and placed inside a ceramic box, and when the thermal fuse senses that the temperature of the wirewound resistor reaches the rated temperature of the thermal fuse, the thermal fuse will melt to cut off the circuit. However, thermal fuse occupies additional area in the PCB and it needs 4 bonding pads under such operation.
Moreover, according to safety consideration, the micro-heating elements used in daily life, such as aromatherapy diffuser or mosquito repellant electric liquid vaporizer, are applied with a thermal fuse against over-heating. Existing assembly method is to connect a resistor and a thermal fuse in series then assemble the unit inside a ceramic box, and the box is filled with solidifiable insulation material. This makes the size of the product large, therefore the heat may be lost and the energy may be wasted.
In addition, the current of the motor of a power tool or an electrical fan is six times the normal working current when they are blocked, under which condition the motor heats quickly. It needs a thermal fuse to cut off the current to prevent a fire because of over-heating condition. But not expected to decrease the operation temperature of the thermal fuse to increase the agility. However, mild overload or voltage pulsation happens when the motor works, under these mild conditions, the thermal fuse is expected not to be cut off. So there is an issue with setting up the temperature of the thermal fuse.
A component comprising a thermal fuse and a resistor of new, small size, an integrated structure and fast installation is provided, the structure solves above three problems.